Metallization  of solar cells with differentiated p-type and n-type region architectures

ABSTRACT

Methods of fabricating solar cell emitter regions with differentiated P-type and N-type regions architectures, and resulting solar cells, are described. In an example, a back contact solar cell can include a substrate having a light-receiving surface and a back surface. A first polycrystalline silicon emitter region of a first conductivity type is disposed on a first thin dielectric layer disposed on the back surface of the substrate. A second polycrystalline silicon emitter region of a second, different, conductivity type is disposed on a second thin dielectric layer disposed on the back surface of the substrate. A third thin dielectric layer is disposed over an exposed outer portion of the first polycrystalline silicon emitter region and is disposed laterally directly between the first and second polycrystalline silicon emitter regions. A first conductive contact structure is disposed on the first polycrystalline silicon emitter region. A second conductive contact structure is disposed on the second polycrystalline silicon emitter region. Metallization methods, include etching techniques for forming a first and second conductive contact structure are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/089,382, filed on Apr. 1, 2016, the entire contents of which arehereby incorporated by reference herein.

BACKGROUND

Photovoltaic (PV) cells, commonly known as solar cells, are devices forconversion of solar radiation into electrical energy. Generally, solarradiation impinging on the surface of, and entering into, the substrateof a solar cell creates electron and hole pairs in the bulk of thesubstrate. The electron and hole pairs migrate to p-doped and n-dopedregions in the substrate, thereby creating a voltage differentialbetween the doped regions. The doped regions are connected to theconductive regions on the solar cell to direct an electrical currentfrom the cell to an external circuit. When PV cells are combined in anarray such as a PV module, the electrical energy collected from all ofthe PV cells can be combined in series and parallel arrangements toprovide power with a certain voltage and current.

Efficiency is an important characteristic of a solar cell as it isdirectly related to the capability of the solar cell to generate power.Likewise, efficiency in producing solar cells is directly related to thecost effectiveness of such solar cells. Accordingly, techniques forincreasing the efficiency of solar cells, or techniques for increasingthe efficiency in the manufacture of solar cells, are generallydesirable. Some embodiments of the present disclosure allow forincreased solar cell manufacture efficiency by providing novel processesfor fabricating solar cell structures. Some embodiments of the presentdisclosure allow for increased solar cell efficiency by providing novelsolar cell structures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a portion of a back contactsolar cell, according to some embodiments.

FIG. 2 is a flowchart listing operations in a method of fabricating asolar cell corresponding to FIGS. 5-16 according to some embodiments.

FIG. 3 is a flowchart listing operations in a patterning process for asolar cell corresponding to FIGS. 11-13, according to some embodiments.

FIG. 4 is a flowchart listing operations in another patterning processfor a solar cell corresponding to FIGS. 14-16, according to someembodiments.

FIGS. 5-10 illustrate cross-sectional views of various stages in thefabrication of a solar cell, according to some embodiments.

FIGS. 11-13 illustrate cross-sectional views in a patterning process fora solar cell, according to some embodiments.

FIGS. 14-16 illustrate cross-sectional views of various stages inanother patterning process for a solar cell, according to someembodiments.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter of theapplication or uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

This specification includes references to “one embodiment” or “anembodiment.” The appearances of the phrases “in one embodiment” or “inan embodiment” do not necessarily refer to the same embodiment.Particular features, structures, or characteristics may be combined inany suitable manner consistent with this disclosure.

Terminology. The following paragraphs provide definitions and/or contextfor terms found in this disclosure (including the appended claims):

“Comprising.” This term is open-ended. As used in the appended claims,this term does not foreclose additional structure or steps.

“Configured To.” Various units or components may be described or claimedas “configured to” perform a task or tasks. In such contexts,“configured to” is used to connote structure by indicating that theunits/components include structure that performs those task or tasksduring operation. As such, the unit/component can be said to beconfigured to perform the task even when the specified unit/component isnot currently operational (e.g., is not on/active). Reciting that aunit/circuit/component is “configured to” perform one or more tasks isexpressly intended not to invoke 35 U.S.C. §112, sixth paragraph, forthat unit/component.

“First,” “Second,” etc. As used herein, these terms are used as labelsfor nouns that they precede, and do not imply any type of ordering(e.g., spatial, temporal, logical, etc.). For example, reference to a“first” silicon region does not necessarily imply that this siliconregion is the first silicon region in a sequence; instead the term“first” is used to differentiate this silicon region from anothersilicon region (e.g., a “second” silicon region). In an example, asilicon region can be a polycrystalline silicon emitter region. In oneexample, a first silicon region can be a first polycrystalline siliconemitter region, where multiple silicon regions can be formed (e.g., asecond silicon region, a second polycrystalline silicon emitter region).

“Based On.” As used herein, this term is used to describe one or morefactors that affect a determination. This term does not forecloseadditional factors that may affect a determination. That is, adetermination may be solely based on those factors or based, at least inpart, on those factors. Consider the phrase “determine A based on B.”While B may be a factor that affects the determination of A, such aphrase does not foreclose the determination of A from also being basedon C. In other instances, A may be determined based solely on B.

“Coupled”—The following description refers to elements or nodes orfeatures being “coupled” together. As used herein, unless expresslystated otherwise, “coupled” means that one element/node/feature isdirectly or indirectly joined to (or directly or indirectly communicateswith) another element/node/feature, and not necessarily mechanically.

“Inhibit”—As used herein, inhibit is used to describe a reducing orminimizing effect. When a component or feature is described asinhibiting an action, motion, or condition it may completely prevent theresult or outcome or future state completely. Additionally, “inhibit”can also refer to a reduction or lessening of the outcome, performance,and/or effect which might otherwise occur. Accordingly, when acomponent, element, or feature is referred to as inhibiting a result orstate, it need not completely prevent or eliminate the result or state.

In addition, certain terminology may also be used in the followingdescription for the purpose of reference only, and thus are not intendedto be limiting. For example, terms such as “upper”, “lower”, “above”,and “below” refer to directions in the drawings to which reference ismade. Terms such as “front”, “back”, “rear”, “side”, “outboard”, and“inboard” describe the orientation and/or location of portions of thecomponent within a consistent but arbitrary frame of reference which ismade clear by reference to the text and the associated drawingsdescribing the component under discussion. Such terminology may includethe words specifically mentioned above, derivatives thereof, and wordsof similar import.

In the following description, numerous specific details are set forth,such as specific operations, in order to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to one skilled in the art that embodiments of the presentdisclosure may be practiced without these specific details. In otherinstances, well-known techniques are not described in detail in order tonot unnecessarily obscure embodiments of the present disclosure.

Methods of fabricating solar cell emitter regions with differentiatedP-type and N-type region architectures, and the resulting solar cells,are described herein. In the following description, numerous specificdetails are set forth, such as specific process flow operations, inorder to provide a thorough understanding of embodiments of the presentdisclosure. It will be apparent to one skilled in the art thatembodiments of the present disclosure may be practiced without thesespecific details. In other instances, well-known fabrication techniques,such as lithography and patterning techniques, are not described indetail in order to not unnecessarily obscure embodiments of the presentdisclosure. Furthermore, it is to be understood that the variousembodiments shown in the figures are illustrative representations andare not necessarily drawn to scale.

Disclosed herein are solar cells. In one embodiment, a back contactsolar cell includes a substrate having a light-receiving surface and aback surface. In an embodiment, a first polycrystalline silicon emitterregion of a first conductivity type is disposed on a first thindielectric layer disposed on the back surface of the substrate. In oneembodiment, a second polycrystalline silicon emitter region of a second,different, conductivity type is disposed on a second thin dielectriclayer disposed on the back surface of the substrate. In an example, thefirst conductivity type can be P-type and the second conductivity typecan be N-type. In an embodiment, a third thin dielectric layer isdisposed over an exposed outer portion of the first polycrystallinesilicon emitter region and is disposed laterally directly between thefirst and second polycrystalline silicon emitter regions. In anembodiment, a first conductive contact structure is disposed on thefirst polycrystalline silicon emitter region. In one embodiment, asecond conductive contact structure is disposed on the secondpolycrystalline silicon emitter region.

In an example, FIG. 1 illustrates a cross-sectional view of a portion ofa back contact solar cell 100, according to some embodiments. In anembodiment, the solar cell 100 can include a substrate 106 having alight-receiving surface 102 and a back surface 104. In one embodiment, afirst polycrystalline silicon emitter region 108 of a first conductivitytype can be disposed on a first thin dielectric layer 114 disposed onthe back surface 104 of the substrate 106. In a specific embodiment, thefirst conductivity type is P-type (e.g., formed using boron impurityatoms). In an embodiment, a second polycrystalline silicon emitterregion 112 of a second, different, conductivity type can be disposed ona second thin dielectric layer 120 disposed on the back surface 104 ofthe substrate 106. In a specific embodiment, the second conductivitytype is N-type (e.g., formed using phosphorus atoms or arsenic impurityatoms). In one embodiment, a third thin dielectric layer 116, 118 can bedisposed over 118 an exposed outer portion 117 of the firstpolycrystalline silicon emitter region and can be disposed laterally 116over a lateral portion 115 of the first polycrystalline silicon,directly between the first 108 and second 112 polycrystalline siliconemitter regions. In an embodiment, a first conductive contact structure128 can be disposed over the first polycrystalline silicon emitterregion 108. In an embodiment, a second conductive contact structure 129can be disposed over the second polycrystalline silicon emitter region112. In an embodiment, the first and second conductive contacts 128, 129can include a plated metal. In one example, the first and secondconductive contacts 128, 129 can include copper, tin, and nickel, amongother metals. In some embodiments, the first and second conductivecontacts 128, 129 can include a metal foil. In an example, the first andsecond conductive contacts 128, 129 can include aluminum or aluminumfoil. In an embodiment, a separation region 124 can separate the firstconductive contact structure 128 from the second conductive contactstructure 129. In some embodiments, a laser ablation process can be usedto separate 124 the first conductive contact structure 128 from thesecond conductive contact structure 129

Referring again to FIG. 1, in an embodiment, the solar cell 100 canfurther include an insulator layer 110 disposed on the firstpolycrystalline silicon emitter region 108. In one example, theinsulator layer 110 can be an oxynitride or a nitride. In an embodiment,the first conductive contact structure 128 can be disposed through theinsulator layer 110. In one embodiment, a portion 111 of the secondpolycrystalline silicon emitter region of the second conductivity typecan overlap the insulator layer 110 but is separate from the firstconductive contact structure 128. In an embodiment, the portion 111 ofthe second polycrystalline silicon emitter region of the secondconductivity type can be disposed on the insulator layer 110, and thefirst conductive contact structure 128 can be disposed through thepolycrystalline silicon layer 111 of the second conductivity type andthrough the insulator layer 110, as is depicted in FIG. 1. In oneembodiment, the portion 111 of the second polycrystalline siliconemitter region and the second polycrystalline silicon emitter region 112can be formed from a same layer that is blanket deposited.

With reference to FIG. 1, an additional silicon region 113 can bedisposed on the second polycrystalline silicon emitter regions 111, 112.In an embodiment, the additional silicon region 113 can be amorphoussilicon or silicon nitride. In one embodiment, the additional siliconregion 113 can be a passivation region and/or an anti-reflective coating(ARC). In some embodiments, the additional silicon region 113 need notbe formed.

Referring again to FIG. 1, in an embodiment, the solar cell 100 furtherincludes a recess 131 disposed in the back surface 104 of the substrate106. In an embodiment, the second polycrystalline silicon emitter region112 and the second thin dielectric layer 120 can be disposed in therecess 131. In one such embodiment, the recess 131 can have a texturizedsurface, and the second polycrystalline silicon emitter region 112 andthe second thin dielectric layer 120 can be conformal with thetexturized surface, as is depicted in FIG. 1. In an embodiment, thefirst polycrystalline silicon emitter region 108 and the first thindielectric layer 114 are disposed on a flat portion of the back surface104 of the substrate 106, and the second polycrystalline silicon emitterregion 112 and the second thin dielectric layer 120 are disposed on atexturized portion of the back surface 104 of the substrate 106, as isdepicted in FIG. 1. It is to be appreciated, however, that otherembodiments may not include a texturized surface, or may not include arecess altogether.

Referring once again to FIG. 1, in an embodiment, the solar cell 100further includes a fourth thin dielectric layer 132 disposed on alight-receiving surface 130 of the substrate 106. A polycrystallinesilicon layer 134 of the second conductivity type can be disposed on thefourth thin dielectric layer 132. An anti-reflective coating (ARC) layer135, such as a layer of silicon nitride, can be disposed on thepolycrystalline silicon layer 134. In one such embodiment, the fourththin dielectric layer 132 can be formed by essentially the same processused to form the second thin dielectric layer 120 and/or the third thindielectric layer 116, 118. In an embodiment, the polycrystalline siliconlayer 134 can be formed by essentially the same process used to form thesecond polycrystalline silicon emitter regions 111, 112.

In some embodiments, the first polycrystalline silicon emitter region108 can be a P-type polycrystalline silicon emitter region. In oneembodiment, the second polycrystalline silicon emitter region 112 can bean N-type polycrystalline silicon emitter region. In an embodiment, thesubstrate 106 can be an N-type monocrystalline silicon substrate. In anembodiment, the first thin dielectric layer 114, the second thindielectric layer 120 and the third thin dielectric layer 116, 118 caninclude silicon dioxide. However, in another embodiment, the first thindielectric layer 114 and the second thin dielectric layer 120 includesilicon dioxide, while the third thin dielectric layer 116, 118 includessilicon nitride. In an embodiment, insulator layer 110 includes silicondioxide.

In an embodiment, a metal seed layer 126, 127 can be disposed betweenthe first and second polycrystalline silicon emitter regions 108, 112and the first and second conductive contact structures 128, 129. In anembodiment, the first and second conductive contact structure 128, 129can include portions 126, 127 of the metal seed layer, respectively. Inan embodiment, the metal seed layer 126, 127 can be an aluminum-basedmetal seed layer. In one such embodiment, the aluminum-based metal seedlayer can have a thickness approximately in the range of 0.3 to 20microns and include aluminum in an amount greater than approximately 97%and silicon in an amount approximately in the range of 0-2%. In anexample, the metal seed layer 126, 127 can include copper, titanium,titanium tungsten, nickel, and/or aluminum, among other metals. In anembodiment, the metal seed layer 126, 127 is formed from a blanketdeposition process. In an embodiment, a first and second portion 126,127 of the metal seed layer can be disposed over the first 108 andsecond 112 polycrystalline silicon emitter regions, respectively. In oneembodiment, each of the first conductive contact structure 128 and thesecond conductive contact structure 129 can include copper, tin, nickel,and/or aluminum, among other metals.

Disclosed herein are methods of fabricating solar cells. In an exemplaryprocess flow, FIGS. 5-16 illustrate cross-sectional views of variousstages in the fabrication of a solar cell, in accordance with anembodiment of the present disclosure. FIG. 2 is a flowchart 200 listingoperations in a method of fabricating a solar cell corresponding toFIGS. 5-16, according to some embodiments. In various embodiments, themethod of FIG. 2 can include additional (or fewer) blocks thanillustrated. For example, in some embodiments, a metal seed layer neednot be formed at block 216, where conductive contacts can instead beformed directly on a back surface of the solar cell.

Disclosed herein are patterning processes for solar cells. In a oneexemplary process flow, FIGS. 11-13 illustrate cross-sectional views ofvarious stages in the formation of conductive contacts of a solar cell,in accordance with an embodiment of the present disclosure. FIG. 3 is aflowchart 300 listing operations in one patterning process of a solarcell corresponding to FIGS. 11-13, according to some embodiments.

Also, disclosed herein is another patterning process for a solar cell.In a an exemplary process flow, FIGS. 14-16 illustrate cross-sectionalviews of various stages in the formation of conductive contacts of asolar cell, in accordance with an embodiment of the present disclosure.FIG. 4 is a flowchart 400 listing operations in a patterning process ofa solar cell corresponding to FIGS. 14-16, according to someembodiments.

Referring to FIG. 5 and corresponding operation 202 of flowchart 200, amethod of fabricating alternating N-type and P-type emitter regions of asolar cell can include forming a first silicon layer 505 of a firstconductivity type on a first thin dielectric layer 514 formed on a backsurface 504 of a substrate 506.

In an embodiment, the substrate 506 can be a monocrystalline siliconsubstrate, such as a bulk single crystalline N-type doped siliconsubstrate. It is to be understood, however, that substrate 506 may be alayer, such as a multi-crystalline silicon layer, disposed on a globalsolar cell substrate. In an embodiment, the substrate 506 can have afront side 502 and a back side 504, where the front side 502 is oppositethe back side 504. In one embodiment, the front side 502 can be referredto as a light receiving surface 502 and the back side can be referred toas a back surface 504. In an embodiment, the first thin dielectric layer514 can be a thin oxide layer such as a tunnel dielectric silicon oxidelayer having a thickness of approximately 2 nanometers or less.

In an embodiment, the first silicon layer 505 can be a polycrystallinesilicon layer that is doped to have the first conductivity type eitherthrough in situ doping, post deposition implanting, or a combinationthereof. In another embodiment, the first silicon layer 505 can be anamorphous silicon layer such as a hydrogenated silicon layer representedby a-Si:H which is implanted with dopants of the first conductivity typesubsequent to deposition of the amorphous silicon layer. In one suchembodiment, the first silicon layer 505 can be subsequently annealed (atleast at some subsequent stage of the process flow) to ultimately form apolycrystalline silicon layer. In an embodiment, for either apolycrystalline silicon layer or an amorphous silicon layer, if postdeposition implantation can be performed, the implanting is performed byusing ion beam implantation or plasma immersion implantation. In onesuch embodiment, a shadow mask can be used for the implanting. In aspecific embodiment, the first conductivity type is P-type (e.g., formedusing boron impurity atoms).

Referring again to FIG. 5 and now to corresponding operation 204 offlowchart 200, an insulating layer 509 can be formed on the firstsilicon layer 505. In an embodiment the insulating layer 509 can besilicon dioxide. In an example, a deposition process can be performed toform the first silicon layer 505.

Referring to FIG. 6 and corresponding operation 206 of flowchart 200,the insulating layer 509 and the first silicon layer 505 of FIG. 5 canbe patterned to form a first silicon region 508 of the firstconductivity type having an insulating cap 510 thereon. In anembodiment, the insulating cap 510 can be formed from the patterning theinsulating layer 509. In an embodiment, a lithographic or screen printmasking and subsequent etch process can be used to pattern theinsulating layer 509 and the first silicon layer 505. In anotherembodiment, a laser ablation process (e.g., direct write) can be used topattern the insulating layer 509 and the first silicon layer 505. Ineither case, in one embodiment, the first thin dielectric layer 514 canalso be patterned in an etching process. In an embodiment, thepatterning can include forming an exposed outer portion 517 and alateral portion 515 of the first silicon region 508.

Referring to FIG. 7, optionally, recesses 503 may be formed in thesubstrate 506 during (or subsequent to) the patterning of the insulatinglayer 509 and the first silicon layer 505. Furthermore, in oneembodiment, the surfaces 503 of the recesses 541 can be texturized. In asame or similar process, a light receiving surface 530 of the substrate506 can also be texturized, as is depicted in FIG. 7. In an embodiment,a hydroxide-based wet etchant can be used to form at least a portion ofthe recesses 503 and/or to texturize exposed portions of the substrate506. A texturized surface may be one which has a regular or an irregularshaped surface for scattering incoming light, decreasing the amount oflight reflected off of the light-receiving and/or exposed surfaces ofthe solar cell. It is to be appreciated, however, that the texturizingof the back surface and even the recess formation may be omitted fromthe process flow.

Referring to FIG. 8 and corresponding operation 208 of flowchart 200, asecond thin dielectric layer 520 can be formed on the back surface 504of the substrate 506. In an embodiment, the second thin dielectric layer520 can be formed in an oxidation process and is a thin oxide layer suchas a tunnel dielectric layer (e.g., silicon oxide). In one embodiment,the second thin dielectric layer 520 can be formed in a depositionprocess. In an embodiment, the second thin dielectric layer 520 is athin oxide layer or silicon oxynitride layer. In an embodiment, thesecond thin dielectric layer can have a thickness of approximately 2nanometers or less.

Referring again to FIG. 8 and now to corresponding operation 210 offlowchart 200, in an embodiment, a first portion 516 of the third thindielectric layer can be formed on the lateral portions 515 of the firstsilicon region 508. In one embodiment, a second portion 518 of the ofthird thin dielectric layer can be formed on the exposed outer portions517 of the first silicon region 508. In an embodiment, the third thindielectric layer can include the first and second 516, 518 portions. Inone embodiment, the third thin dielectric layer 516, 518 can be formedin an oxidation process and can be a thin oxide layer such as a tunneldielectric layer (e.g., silicon oxide). In an embodiment, the third thinoxide layer can have a thickness of approximately 3 nanometers or less.In one embodiment, the third thin dielectric layer 516, 518 can beformed in a deposition process. In an embodiment, the third thindielectric layer 516, 518 can be a thin oxide layer or siliconoxynitride layer. In an embodiment, the second and third thin dielectriclayers 520, 516, 518 can be formed in the same oxidation and/ordeposition process.

Referring once again to FIG. 8 and now to corresponding operation 212 offlowchart 200, a second silicon layer 507 of a second, different,conductivity type can be formed on the third thin dielectric layer 516,518, on the second thin dielectric layer 520 and on the insulating cap510 of the first silicon regions 508. In an embodiment, correspondingthin dielectric layer 532 and second silicon layer 534 of the secondconductivity type can be formed on the light-receiving surface 530 ofthe substrate 506, in the same or similar process operations used toform the second silicon layer 507, second thin dielectric layer 520 andthird thin dielectric layer 516, 518, as is depicted in FIG. 8.Additionally, although not depicted, an anti-reflective (ARC) layer maybe formed on the corresponding second silicon layer 534, as described inassociation with FIG. 1. In an embodiment, the second silicon layer 507can be a polycrystalline silicon layer that is doped to have the secondconductivity type either through in situ doping, post depositionimplanting, or a combination thereof. In another embodiment, the secondsilicon layer 507 can be an amorphous silicon layer such as ahydrogenated silicon layer represented by a-Si:H which is implanted withdopants of the second conductivity type subsequent to deposition of theamorphous silicon layer. In one such embodiment, the second siliconlayer 507 can be subsequently annealed (at least at some subsequentstage of the process flow) to ultimately form a polycrystalline siliconlayer. In an embodiment, for either a polycrystalline silicon layer oran amorphous silicon layer, if post deposition implantation isperformed, the implanting can be performed by using ion beamimplantation or plasma immersion implantation. In one such embodiment, ashadow mask can be used for the implanting. In a specific embodiment,the second conductivity type is N-type (e.g., formed using phosphorusatoms or arsenic impurity atoms). Additionally, although not depictedand subsequent to forming the second silicon layer 507, an additionalsilicon region can be formed on the second silicon layer 507 asdescribed in association with FIG. 1. In one embodiment, the additionalsilicon region can be amorphous silicon or silicon nitride. In someembodiments, the additional silicon region can be a passivation regionand/or an anti-reflective coating (ARC). In some embodiments, theadditional silicon region need not be formed.

Referring again to FIG. 9 and now to corresponding operation 214 offlowchart 200, the insulating cap 510 can be patterned through thecontact openings 522 to expose portions of the first silicon regions508. In an embodiment, the insulating cap 510 is patterned using a laserablation process. In one embodiment, a first laser pass can be used topattern the second silicon layer 507, including forming contact opening522. In an embodiment, subsequent to performing first laser pass, asecond laser pass in the same location as contact opening 522 can be theused to pattern the insulating cap 510.

Referring again to FIG. 10 and now to corresponding operation 216 offlowchart 200, at metal seed layer 525 can be formed over the firstsilicon regions 508 and second silicon layer 507. In an embodiment, adeposition process can be performed to form the metal seed layer 525. Inan example, a sputtering process can be used to form the metal seedlayer 525. In one example, the metal seed layer 5257 is formed from ablanket deposition process. In an embodiment, the metal seed layer 525can include one or more metals and/or metal alloys. In an example, themetal seed layer can include aluminum, titanium tungsten and/or copper,among other metals. In an embodiment, the metal seed layer 525 caninclude one, two or more layers. In an example, the metal seed layer 525can include a first layer including copper, a second layer includingtungsten and a third layer including aluminum. In some embodiments, analuminum portion of the metal seed layer 525 can be disposed over thefirst silicon regions 508 and second silicon layer 507.

In some embodiments, the metal seed layer 525 need not be formed. In oneexample, a metal layer can instead be formed on, and directlycontacting, the first silicon regions 508 and second silicon layer 507.

Referring to FIGS. 11-16 and now to corresponding operation 218 offlowchart 200, a patterning process can be performed. In an embodiment,the patterning process can include forming isolated second siliconregions of a second conductivity type. In one embodiment, the patterningprocess can include forming a first conductive contact for the firstsilicon regions and a second conductive contact for the isolated secondsilicon regions. In an embodiment, the patterning process can includeperforming a laser ablation process.

In an exemplary process flow, FIGS. 11-13 illustrate cross-sectionalviews of various stages in one example patterning process for a solarcell, in accordance with an embodiment of the present disclosure. In anembodiment, the patterning process of FIGS. 11-13 can include performinga plating and etching process. In an exemplary process flow, FIGS. 14-16illustrate cross-sectional views of various stages in another patterningprocess for a solar cell, in accordance with an embodiment of thepresent disclosure. In an embodiment, the patterning process of FIGS.14-16 can include performing a metal foil based bonding and etchingprocess.

In an exemplary process flow, FIG. 3 is a flowchart 300 listingoperations in a patterning process for a solar cell corresponding toFIGS. 11-13, according to some embodiments. In various embodiments, themethod of FIG. 3 can include additional (or fewer) blocks thanillustrated. For example, in some embodiments, a mask need not beremoved at block 306, where the mask can instead be removed during apatterning process at block 308. Accordingly, the exemplary process flowmoves from the structure of FIG. 10 to the structure of FIG. 11.

Referring to FIG. 11 and corresponding operation 302 of flowchart 300, amask 536 can be formed over a metal seed layer 525, according to someembodiments. In an embodiment, the mask 536 can protect portions 550 ofthe metal seed layer 525 during a subsequent plating process, whileexposed regions 552 can be plated during said plating process. In anembodiment, the mask 536 can be formed by screen printing, inkjetprinting, among other printing processes. In one embodiment, the mask536 can be an etch resist. In one embodiment, the etch resist can be anetch resist 536 commonly used in the fabrication or manufacture of solarcells. In some embodiments, the etch resist 536 is a plating resist.

Referring to FIG. 12 and corresponding operation 304 of flowchart 300, ametal layer 528 can be formed on exposed portions 552 of the metal seedlayer 525. In an embodiment, a plating process can be performed to formthe metal layer 528 on exposed portions 552 of the metal seed layer 525,where the mask 536 can protect portions 550 of the metal seed layerduring the plating process. In an example, copper, tin, and/or nickel,among other metals, can be plated to exposed portions 552 of the metalseed layer 525.

Referring to FIG. 13 and corresponding operation 306 of flowchart 300,the mask 536 of FIG. 12 can be removed. In an embodiment, the mask 536can be removed using a wet chemical process. In an example, an inkstripping process can be performed to remove the mask 536.

Referring again to FIG. 13 and corresponding operation of flowchart 308,the metal seed layer 525 and second silicon layer 507 of FIG. 12 can bepatterned to form isolated second silicon regions 511, 512 of the secondconductivity type and to form conductive contacts 538, 539 for the firstsilicon regions 508 and the isolated second silicon regions 512,respectively. In an embodiment, the patterning can include etching themetal seed layer 525 and second silicon layer 507 of FIG. 12 to formisolated second silicon regions 511, 512 of the second conductivity typeand to form conductive contacts 538, 539 for the first silicon regions508 and the isolated second silicon regions 512. In an embodiment, theetching includes etching the metal seed layer 525 and/or second siliconlayer 507 of FIG. 12 using one or more etchants. In an embodiment, ahydroxide-based wet etchant can be used. In one example, the etchant caninclude potassium hydroxide, tetramethylammonium hydroxide, ammoniumhydroxide and/or sodium hydroxide. In some embodiments, the etchant caninclude an etchant having a weight percent of greater than 2% potassiumhydroxide.

In an embodiment, referring to FIGS. 12 and 13, a first etchant can beused to etch the metal seed layer 525. In an example, the first etchantcan be potassium hydroxide. In an embodiment, subsequent to etching themetal seed layer 525 using a first etchant, a second etchant can be usedto etch the second silicon layer 507. In one embodiment, the firstand/or the second etchant can be an alkaline etchant. In an embodiment,the second etchant can include an oxidizer. In an embodiment, theoxidizer can inhibit etching of the metal seed layer 525. In oneembodiment, the oxidizer can inhibit undercutting of the metal seedlayer 525. In an example, during the etching of the second silicon layer507, the oxidizer can inhibit etching of lateral portions 543 of themetal seed layer 525 to prevent substantial undercutting at regionsadjacent to the etching of the second silicon layer 507. In one example,the patterning can include etching an aluminum-based metal seed layer525 using potassium hydroxide. Subsequent to etching the aluminum-basedmetal seed layer 525, the patterning can include etching the secondsilicon layer 507, where the oxidizer can inhibit etching of lateralportions 543 of the aluminum-based metal seed layer 525 during theetching process. In an example, the patterning can include etching thesecond silicon layer 507 using potassium hydroxide. In an embodiment,the oxidizer can be hydrogen peroxide and/or ammonium peroxodisulphate.

In an embodiment, the etching can include etching at a temperature inthe range of 40-80 degrees Celsius. In an embodiment, referring to FIG.12 and subsequent to removing the mask 536, the etching can etchportions 550 of the metal seed layer 525, where the metal layer 528 canprevent etching other portions 552 of the metal seed layer 525 duringthe etching process.

In an embodiment, the metal seed layer 525 can include one, two or moreportions. In an example, the metal seed layer 525 can include a firstportion including copper, a second layer including tungsten and a thirdlayer including aluminum. In an embodiment, the first, second, thirdportions, among other portions, can also be referred to as a first,second, third layer, among other layers.

In an embodiment, the etching can include etching a first portion of themetal seed layer 525. In an example, the etching can include etching acopper portion of the metal seed layer. Subsequent to etching the firstportion, the etching can include etching a second portion of the metalseed layer. In one example, subsequent to etching a copper portion ofthe metal seed layer, the etching can include etching an aluminumportion of the metal seed layer. In an embodiment, the aluminum portionof the metal seed layer 525 can be disposed over the first siliconregions 508 and second silicon layer 507. In an embodiment, etching thesecond portion of the metal seed layer can include etching a secondportion of the metal seed layer and the second silicon layer 507 withthe same etchant and/or etching both layers at the same etching processstep. In an example, the etching can include etching an aluminum portionof the metal seed layer and an n-type doped silicon layer using the sameetchant, where the aluminum portion of the metal seed layer is disposedon the n-type doped silicon layer.

Referring once again to FIG. 13, a solar cell 500 is shown fabricatedusing the methods of FIGS. 1-13 and corresponding to the operations ofthe flowcharts 200 and 300 of FIGS. 2 and 3, respectively. As shown, thesolar cell 500 of FIG. 13 has similar reference numbers to elements ofthe solar cell 100 of FIG. 1, where like reference numbers refer tosimilar elements throughout the figures. In an embodiment, the structureof the solar cell 500 of FIG. 5 is substantially similar to thestructure of the solar cell 100 of FIG. 1, except as described above.Therefore the description of corresponding portions of FIG. 1 appliesequally to the description of FIG. 13. In an example, referring to FIG.13 and FIG. 1, the first silicon region 508 can correspond to the firstpolycrystalline silicon emitter region 108. In one example, referringagain to FIG. 13 and FIG. 1, the second isolated silicon regions 526,527 can correspond to the second polycrystalline silicon emitter regions126, 127.

In an exemplary process flow, FIG. 4 is a flowchart 400 listingoperations in another patterning process for a solar cell correspondingto FIGS. 14-16, according to some embodiments. Accordingly, theexemplary process flow moves from the structure of FIG. 10 to thestructure of FIG. 14. As shown, the solar cell of FIGS. 14-16 havesimilar reference numbers to elements of the solar cell of FIGS. 1-13,where like reference numbers refer to similar elements throughout thefigures. In an embodiment, the structure of the solar cell of FIGS.14-16 is substantially similar to the structure of the solar cell ofFIGS. 1-13, except as described below. Therefore the description ofcorresponding portions of FIGS. 1-13 applies equally to the descriptionof FIG. 14-16, except as described below. In various embodiments, themethod of FIG. 4 can include additional (or fewer) blocks thanillustrated. For example, in some embodiments, a mask need not beremoved block 410.

Referring to FIG. 14 and corresponding operation 402 of flowchart 400, ametal layer 640 can be formed over a metal seed layer 625. In anembodiment, forming the metal layer 640 can include placing a metal foil640 over a metal seed layer 625. In an example, aluminum (e.g., aluminumfoil) can be placed over the metal seed layer 625. In an embodiment,placing the metal foil 640 over the metal seed layer 625 can includeperforming compression process to place the metal foil 640 onto themetal seed layer 625. In some embodiments, a metal seed layer 625 neednot be formed, where the metal foil 640 can be placed directly on afirst silicon region 608 and/or second silicon layer 607.

Referring again to FIG. 14 and corresponding operation 404 of flowchart400, the metal layer 640 can be bonded to the metal seed layer 625. Inan embodiment, bonding the metal layer 640 to the metal seed layer caninclude bonding a metal foil 640 to the metal seed layer 625. In anembodiment, the bonding can including welding the metal foil 640 to themetal seed layer 625. In some embodiments, a laser can be used to bondto the metal foil 640 to the metal seed layer 625. In an example, alaser welding process can be used to bond to the metal foil 640 to themetal seed layer 625. In some embodiments, the metal foil 640 can bebonded directly to the first silicon region 608 and/or second siliconlayer 607.

Referring to FIG. 15 and corresponding operation 406 of flowchart 400, amask 636 can be formed over the metal layer 640, according to someembodiments. In an embodiment, forming the mask 636 can include formingthe mask over a metal foil 640. In an embodiment, the mask 636 canprotect portions 650 of the metal foil 640 during a subsequent etchingprocess, while exposed regions 652 can be etched during said etchingprocess. In an embodiment, the mask 636 can be formed by screenprinting, inkjet printing, among other printing processes. In oneembodiment, the mask 636 can be an etch resist. In one embodiment, themask 636 can be a etch resist commonly used in the fabrication ormanufacture of solar cells.

Referring to FIG. 16 and corresponding operation 408 of flowchart 400,the metal layer 640 and second silicon layer 607 can be patterned toform isolated second silicon regions 611, 612 of the second conductivitytype and to form conductive contacts 638, 639 for the first siliconregions 608 and the isolated second silicon regions 512, respectively.In an embodiment, patterning the metal layer can include patterning ametal foil 640. In an embodiment, the patterning can include etchingexposed portions 650 of the metal foil 640, metal seed layer 625 andsecond silicon layer 607 to form isolated second silicon regions 611,612 of a second conductivity type to form conductive contacts 638, 639for the first silicon regions 608 and the isolated second siliconregions 612. In an embodiment, the etching includes etching the metalfoil 640, metal seed layer 625 and second silicon layer 607 using one ormore etchants. In an example, the etchant can include potassiumhydroxide, tetramethylammonium hydroxide, ammonium hydroxide and/orsodium hydroxide. In some embodiments, the etchant can include anetchant having a weight percent of greater than 2% potassium hydroxide.

In an embodiment, the etching includes etching the metal foil 640, metalseed layer 625 and second silicon layer 607 in a single or multipleetching process steps. In an example, the etching process step caninclude etching with one or more etchants. In an embodiment, a firstetchant can be used to etch the metal layer 640 and metal seed layer625. In an example, the first etchant can be potassium hydroxide. In anembodiment, subsequent to etching the metal layer 640 and the metal seedlayer 625 using a first etchant, a second etchant can be used to etchthe second silicon layer 607. In one embodiment, the first and/or secondetchant can be an alkaline etchant. In an embodiment, the second etchantcan include an oxidizer. In an embodiment, the oxidizer can inhibitetching of the metal layer 640 and/or metal seed layer 625. In anexample, the metal layer 640 can be a metal foil 640. In one embodiment,the oxidizer can inhibit undercutting of the metal seed layer 625. In anexample, during the etching of the second silicon layer 607, an oxidizercan inhibit etching of lateral portions 643, 645 of the metal seed layer625 and/or metal foil 640, respectively. In an embodiment, the oxidizercan inhibit etching of lateral portions 643 of the metal seed layer 625to prevent substantial undercutting at regions adjacent to the etchingof the second silicon layer 607. In some embodiments, the metal seedlayer 625 need not be formed where the metal foil 640 can be disposeddirectly over the back surface 604 of the substrate 606. In one example,the patterning can include etching an aluminum foil and analuminum-based metal seed layer using potassium hydroxide. Subsequent toetching an aluminum foil and the aluminum-based metal seed layer 625,the patterning can include etching the second silicon layer 607 using asecond etchant, where the second etchant can include an oxidizer toinhibit etching of lateral portions 643, 645 of an aluminum-based metalseed layer and aluminum foil, respectively. In some embodiments, thealuminum-based metal seed layer need not be formed. In an embodiment,the oxidizer can be hydrogen peroxide and/or ammonium peroxodisulphate.

In an embodiment, the etching can include etching at a temperature inthe range of 40-80 degrees Celsius. In some embodiments, the etching caninclude etching exposed portions of the metal foil 640, metal seed layer625 and second silicon layer 607 of FIG. 12 in a same etching processstep.

Referring again to FIG. 16 and corresponding operation 410 of flowchart400, the mask 636 can be removed. In an embodiment, the mask can beremoved using a wet chemical process. In an example, an ink strippingprocess can be performed to remove the mask 636. In some embodiments,the mask 636 need not be removed.

Referring once again to FIG. 16, a solar cell 600 is shown fabricatedusing the methods of FIGS. 1-10 and 14-16 and corresponding to theoperations of the flowcharts 200 and 400 of FIGS. 2 and 4. As shown, thesolar cell of FIG. 600 of FIG. 16 have similar reference numbers toelements of the solar cell 100 of FIG. 1, where like reference numbersrefer to similar elements throughout the figures. In an embodiment, thestructure of the solar cell 600 of FIG. 16 is substantially similar tothe structure of the solar cell 100 of FIG. 1, except as describedabove. Therefore the description of corresponding portions of FIG. 1applies equally to the description of FIG. 16. In an example, referringto FIG. 16 and FIG. 1, the first silicon region 608 can correspond tothe first polycrystalline silicon emitter region 108. In one example,referring again to FIG. 16 and FIG. 1, the second isolated siliconregions 626, 627 can correspond to the second polycrystalline siliconemitter regions 126, 127.

Although specific embodiments have been described above, theseembodiments are not intended to limit the scope of the presentdisclosure, even where only a single embodiment is described withrespect to a particular feature. Examples of features provided in thedisclosure are intended to be illustrative rather than restrictiveunless stated otherwise. The above description is intended to cover suchalternatives, modifications, and equivalents as would be apparent to aperson skilled in the art having the benefit of this disclosure.

The scope of the present disclosure includes any feature or combinationof features disclosed herein (either explicitly or implicitly), or anygeneralization thereof, whether or not it mitigates any or all of theproblems addressed herein. Accordingly, new claims may be formulatedduring prosecution of this application (or an application claimingpriority thereto) to any such combination of features. In particular,with reference to the appended claims, features from dependent claimsmay be combined with those of the independent claims and features fromrespective independent claims may be combined in any appropriate mannerand not merely in the specific combinations enumerated in the appendedclaims.

What is claimed is:
 1. A back contact solar cell, comprising: asubstrate having a light-receiving surface and a back surface; a firstpolycrystalline silicon emitter region of a first conductivity typedisposed on a first thin dielectric layer disposed on the back surfaceof the substrate; a second polycrystalline silicon emitter region of asecond, different, conductivity type disposed on a second thindielectric layer disposed on the back surface of the substrate; a thirdthin dielectric layer disposed over an exposed outer portion of thefirst polycrystalline silicon emitter region and disposed laterallydirectly between the first and second polycrystalline silicon emitterregions; a first conductive contact structure disposed over the firstpolycrystalline silicon emitter region; and a second conductive contactstructure disposed over the second polycrystalline silicon emitterregion.
 2. The back contact solar cell of claim 1, further comprising:an insulator layer disposed on the first polycrystalline silicon emitterregion, wherein the first conductive contact structure is disposedthrough the insulator layer, and wherein a portion of the secondpolycrystalline silicon emitter region overlaps the insulator layer butis separate from the first conductive contact structure.
 3. The backcontact solar cell of claim 2, wherein the insulator layer comprises anoxynitride or a nitride.
 4. The back contact solar cell of claim 1,further comprising: an amorphous silicon region disposed over the secondpolycrystalline silicon emitter region.
 5. The back contact solar cellof claim 1, further comprising: a silicon nitride region disposed overthe second polycrystalline silicon emitter region.
 6. The back contactsolar cell of claim 1, further comprising: an insulator layer disposedon the first polycrystalline silicon emitter region; and apolycrystalline silicon layer of the second conductivity type disposedon the insulator layer, wherein the first conductive contact structureis disposed through the polycrystalline silicon layer of the secondconductivity type and through the insulator layer.
 7. The back contactsolar cell of claim 1, wherein the second polycrystalline siliconemitter region and the second thin dielectric layer are disposed in arecess disposed in the substrate.
 8. The back contact solar cell ofclaim 7, wherein the recess has a texturized surface.
 9. The backcontact solar cell of claim 1, wherein the first polycrystalline siliconemitter region and the first thin dielectric layer are disposed on aflat portion of the back surface of the substrate, and wherein thesecond polycrystalline silicon emitter region and the second thindielectric layer are disposed on a texturized portion of the backsurface of the substrate.
 10. The back contact solar cell of claim 1,wherein the first and second conductive contact structures eachcomprises an aluminum-based metal seed layer disposed on the first andsecond polycrystalline silicon emitter regions, respectively, and eachfurther comprises a metal layer disposed on the aluminum-based metalseed layer.
 11. The back contact solar cell of claim 1, furthercomprising: a fourth thin dielectric layer disposed on thelight-receiving surface of the substrate; a polycrystalline siliconlayer of the second conductivity type disposed on the fourth thindielectric layer; and an anti-reflective coating (ARC) layer disposed onthe polycrystalline silicon layer of the second conductivity type. 12.The back contact solar cell of claim 1, wherein the substrate is anN-type monocrystalline silicon substrate, the first conductivity type isP-type, and the second conductivity type is N-type.
 13. The back contactsolar cell of claim 1, wherein all of the first, second and third thindielectric layers comprise silicon dioxide.
 14. The back contact solarcell of claim 1, wherein the second polycrystalline silicon emitterregion is disposed on a portion of the third thin dielectric layerdisposed over the exposed outer portion of the first polycrystallinesilicon emitter region.
 15. A back contact solar cell, comprising: asubstrate having a light-receiving surface and a back surface; a P-typeemitter region disposed on a first thin dielectric layer disposed on theback surface of the substrate; an N-type emitter region disposed on asecond thin dielectric layer disposed on the back surface of thesubstrate; a third thin dielectric layer disposed over an exposed outerportion of the P-type emitter region and disposed laterally directlybetween the P-type and the N-type emitter regions; a first conductivecontact structure disposed over the P-type emitter region; and a secondconductive contact structure disposed over the N-type emitter region.16. The back contact solar cell of claim 15, wherein the N-type emitterregion and the second thin dielectric layer are disposed in a recessdisposed in the substrate, and wherein the recess has a texturizedsurface.
 17. The back contact solar cell of claim 15, wherein the N-typeemitter region is disposed on a portion of the third thin dielectriclayer disposed over the exposed outer portion of the P-type emitterregion.
 18. A back contact solar cell, comprising: a substrate having alight-receiving surface and a back surface; an N-type emitter regiondisposed on a first thin dielectric layer disposed on the back surfaceof the substrate; a P-type emitter region disposed on a second thindielectric layer disposed on the back surface of the substrate; a thirdthin dielectric layer disposed over an exposed outer portion of theN-type emitter region and disposed laterally directly between the N-typeand the P-type emitter regions; a first conductive contact structuredisposed over the N-type emitter region; and a second conductive contactstructure disposed over the P-type emitter region.
 19. The back contactsolar cell of claim 18, wherein the P-type emitter region and the secondthin dielectric layer are disposed in a recess disposed in thesubstrate, and wherein the recess has a texturized surface.
 20. The backcontact solar cell of claim 18, wherein the P-type emitter region isdisposed on a portion of the third thin dielectric layer disposed overthe exposed outer portion of the N-type emitter region.